Machine gun

ABSTRACT

The machine gun of this invention features a unitary bolt and bolt drive assembly reciprocably mounted within a receiver along three longitudinally extending bearing supports symmetrically arranged in spaced relation to the receiver; the bolt and bolt drive assembly, together with a recoil buffer constituting and integral operating group removably maintained within the receiver by a single latch mechanism; a bolt carrier of the assembly incorporating actuating means for cartridge belt advance, cartridge extraction and ejection; the bolt carrier housing not only a rotary, front-locking bolt but also a cam follower which fixes a firing pin to the carrier and moves within a contoured slot in the bolt for locking and unlocking it in battery. This machine gun also features a gas recoil system for the bolt and bolt drive assembly having anti-fouling porting means for purging gas from the system under high pressure after firing; an ejector operated by the recoiling bolt and bolt drive assembly independently of its velocity; an automatically engageable, selfaligning barrel and receiver latch construction; and a sight assembly featuring a zero backlash precision screw adjustment means.

United States Patent Curtis et a1.

[54] MACHINE GUN [72] Inventors: George F. Curtis, East Longmeadow; Henry J. Tatro, Jr., Westfield, both of Mass.

[73] Assignee: Colts lnc., Hartford, Conn. 22 Filed: Sept. 12,1969

[21] Appl. No.: 857,479

[52] US. Cl ..89/189, 89/191 6/1970 Stoner ..89/198 Primary Examiner-Stephen C. Bentley Attorney-Prutzman, Hayes, Kalb & Chilton a" 1 Huang 51 Sept. 5, 1972 [57] 7 ABSTRACT The machine gun of this invention features a unitary bolt and bolt drive assembly reciprocably mounted within a receiver along three longitudinally extending bearing supports symmetrically arranged in spaced relation to the receiver; the bolt and bolt drive assembly, together with a recoil buffer constituting and integral operating group removably maintained within the receiver by a single latch mechanism; a bolt carrier of the assembly incorporating actuating means for cartridge belt advance, cartridge extraction and ejection; the bolt carrier housing not only a rotary, frontlocking bolt but also a cam follower which fixes a firing pin to the carrier and moves within a contoured slot in the bolt for locking and unlocking it in battery.

This machine gun also features a gas recoil system for the bolt and bolt drive assembly having anti-fouling porting means for purging gas from the system under high pressure after firing; an ejector operated by the recoiling bolt and bolt drive assembly independently of its velocity; an automatically engageable, self-aligning barrel and receiver latch construction; and a sight assembly featuring a zero backlash precision screw adjustment means.

32 Claims, 11 Drawing Figures PATENTED SEP 5 I972 SHEET 2 BF 3 MACHINE GUN This invention relates to machine guns and particularly concerns air-cooled, disintegrating link belt fed, gas operated machine guns.

A primary object of this invention is to provide an improved machine gun having a mechanical operating and assembly design which significantly simplifies construction, minimizes the number of operating parts with a corresponding reduction in logistical requirements, reduces costs and is rugged and reliable while also being quick and easy to operate and maintain.

Another object of this invention is to provide an improved machine gun having an operating group, including bolt and bolt drive assemblies and a recoil buffer, which is readily removable as a separate unit in a one step operation for facile field maintenance.

Still another object of this invention is the provision of an improved balanced support system for the operating group within the receiver.

A further object of this invention is to provide an improved operating group and associated trigger group incorporating a variety of improved safety features for fail-safe operation of the machine gun.

A still further object of this invention is to provide a machine gun of significantly improved and simplified design featuring a one piece receiver which primarily serves as a cover and incorporates an improved arrangement of operating parts which minimizes repair and service requirements and also facilitates disassembly and reassembly of the machine gun without tools.

Another object of this invention is to provide an improved machine gun incorporating a self-aligning, selflatching quick change barrel minimizing any need for hand protection when changing hot barrels.

A still further object of this invention is to provide a significantly improved bolt assembly suited to be maintained in open battery before firing, which is of a rotary, front locking, multi-lug type and which additionally controls the advance of a cartridge belt as well as positive ejection of spent cartridges through the bottom of the receiver irrespective of the attitude of the gun.

Another object of this invention is the provision of an improved feed system for advancing live rounds in suc cession to a stripping station of a machine gun and which is controlled by reciprocation of the bolt assembly.

Still another object of this invention is to provide an improved machine gun which can be readily charged with a pistol grip mounted for sliding movement on the receiver for either left or right hand operation without need to change or vary the arrangement of the operat ing components.

Another object of this invention is to provide an improved gas recoil system for a machine gun featuring gas purging of the system under relatively high gas pressure.

Still another object of this invention is to provide a machine gun having an improved ejector operated by the driving force of the recoiling mass, independently of its velocity and without requiring a spring as a driving force.

A yet further object of this invention is to provide an improved sight assembly usable in a machine gun and which is particularly suited to effect precision sight adjustment while minimizing any possibility of backlash during such adjustment.

Other objects will be in part obvious and in part pointed out more in detail hereinafter.

A better understanding of the objects, advantages, features, properties and relationships of the invention will be obtained from the following detailed description and accompanying drawings which set forth an illustrative embodiment and are indicative of the ways in which the principle of the invention is employed.

In the drawings:

FIG. 1 is a side view, partly broken away and partly in section, showing a machine gun incorporating the invention;

FIG. 2 is an exploded isometric view, partly broken away, of the machine gun of FIG. 1;

FIG. 3 is an enlarged sectional view taken along line 3-3 of FIG. 1;

. FIG. 4 is an enlarged front view of a bolt face of a bolt assembly of this invention;

FIG. 5 is an enlarged sectional view, partly broken away, taken along line 5-5 of FIG. 1;

FIG. 6 is an enlarged sectional view, partly broken away, showing a machine gun gas porting arrangement embodied in this invention;

FIG. 7 is an enlarged sectional view, partly broken away, showing details of a sight assembly embodied in this invention;

FIG. 8 is a side view of a trigger group safety embodied in the machine gun of this invention; I

' FIG. 9 is an enlarged isometric view, partly broken away, of an actuator lug of the cartridge advancing system of this invention;

FIG. 10 is an enlarged view, partly broken away, of a retaining pawl of the cartridge advancing system; and

FIG. 11 is an enlarged sectional view, partly broken away, showing an ejector of the machine gun of this invention.

Referring to the drawings in detail, a barrel 10 of the machine gun embodying this invention is shown mounted on an elongated, hollow sheet metal receiver 12. A cylinder 14 of a gas recoil system is fitted into a gas porting head 16 shown fixed to the barrel l0 and having an attached, fixed front sight 18. The gas cylinder 14 is removably locked to the receiver 12 by a forward hand grip 20 mounted by a suitable tongue and groove connection to a portion 22 of the cylinder 14 protruding downwardly through a bottom opening 24 in the receiver 12.

For changing hot barrels without requiring hand protection for a gunner, an automatically engageable barrel and receiver latch assembly is provided. A pivotable carrying handle 26 is secured to the barrel 10 which has a rear barrel socket 28 for receipt in a bore 30 of a barrel bearing block 32 fixed in the receiver 12. A boss 34 circumferentially'extends about the barrel 10 and is preferably chamfered along its upper surface for carnming up a smoothly contoured boss engaging lip 36 on the front of a latch 38 pivotally mounted on a crosspin 40 fixed to the block 32. Extending rearwardly of the lip 36 is an upright center web 42 which readily seats within an alignment slot 44 in the boss 34 on the upper portion of the barrel 10 upon passing the boss 34 under the lip 36 into engagement with the block 32. A

coil spring 46 continuously urges the lip 36 downwardly to maintain the barrel in looked assembly with the receiver 12. Thus, the latch 38 automatically aligns and locks the barrel 10 against rotation as well as longitudinal movement relative to the receiver 12. To disassemble, the latch 38 is merely depressed to overcome the spring force and release the barrel 10.

To simplify construction, reduce manufacturing costs and also ensure quick and easy field stripping and maintenance, a unitary bolt and bolt drive assembly together with a recoil buffer has been provided in accordance with this invention in a single operating group 50 which is easily removed as a separate unit from the receiver 12. Moreover, the operating group 50 of this invention not only functions to carry a bolt 52 between open bolt and locked battery positions but additionally controls feeding of live rounds into the barrel 10 and the ejection of spent cartridges through the receiver 12. By virtue of such construction, the interior receiver walls 54, 56 are particularly suited to be substantially free of expensive machining normally required to provide such multiple functions whereby the receiver 12 essentially serves as a simple cover for the operating components.

More specifically, a recoil buffer 58 is secured to a buttstock 60 in operative alignment behind a bolt assembly 62. The recoil buffer 58 is preferably of a hydraulic type. A plunger 64 is provided having an apertured piston 66 received within a liquid filled chamber 68, and an exposed end portion of the plunger 64 is continuously urged by a return spring 70 to project forwardly out of the buffer 58 to absorb shock loading imposed on the gun during recoil of the bolt assembly 62.

To provide a balanced drive system for reciprocating the bolt assembly 62 within the receiver 12 for reliable high performance operation under adverse conditions while at the same time minimizing close tolerance requirements, the bolt assembly 62 is provided with a balanced bearing support arrangement along three symmetrically spaced axes of bearing support. Specifically, the bolt assembly 62 is supported for reciprocating movement on two simple guide rods 72, 74 mounted within outwardly projecting side wall portions 76, 78 of the receiver 12 in outboard parallel relation to the buffer plunger 64. The bolt assembly 62 also includes a gas piston 80 suitably secured to extend forwardly of a bolt carrier 82 of the assembly 62 for reciprocating movement within the gas cylinder 14 which serves to provide a third bearing support means for the bolt assembly 62.

The guide rods 72, 74 extend through apertured side lugs (only one shown at 84 in FIG. 2) in the bolt carrier 82 which is maintained in assembly on the rods 72, 74 by an enlarged forward end portion (shown at 86) on each rod 72, 74 suited to be received in an opening such as at 88 formed in the barrel bearing block 32. A driving spring 90 is coiled about each guide rod 72, 74 between its respective lug 84 and the recoil buffer 58 to which the guide rods 72, 74 are secured.

By virtue of the outboard parallel mounting arrangement of the guide rods 72, 74 relative to the buffer plunger 64, a buffer return spring of lower stiffness may be used and only a minimal amount of energy has to be returned by the buffer plunger 64, sufficient to fully return the plunger for engaging the bolt assembly 62 during its next recoil cycle. Accordingly, shock loading on recoil is reduced and the service life of other associated parts is correspondingly increased.

In the specific illustrated embodiment, each guide rod 72, 74 (FIG. 5) is preferably necked down by a groove 92 adjacent its rear end which is received in a suitable opening 94 in the buffer 58. An apertured plate 96 is fitted into a lateral slot 98 in the buffer 58 communicating with its openings 94 such that opposite side edges of the retaining plate 96 are disposed in interfering relation within the grooves 92 of the rods 72, 74 to lock the same into operative position. The retaining plate 96 may be removably fixed within the buffer 58 by a spring-biased plunger 100 mounted in the buffer 58 to extend through the central opening 102 in the retaining plate 96. The bolt assembly 62 thus may be disassembled from its drive and buffer systems by the simple expedient of merely removing the retaining plate 96.

Another feature embodied in this invention is the provision of a single latching means for maintaining the operating group 50 in its entirety in fixed operative position within the receiver 12. For this purpose a cavity 104 is formed in the buffer 58 in communication with a bottom opening 106 at the rear of the receiver 12. A push-button latch 108 is fitted for pivotal movement within a groove 110 at the forward end of the cavity 104. The latch 108 is suitably dimensioned and configured to bottom against the buffer 58 with a lower portion of the latch 108 protruding outwardly into engagement with the receiver 12 under the force of a leaf spring 112. Rearward movement of the operating group 50 relative to the receiver 12 is thus effectively blocked unless the latch 108 is first pressed inwardly to clear the receiver 12.

Accordingly, only one latch need be depressed to permit the entire operating group 50 to be removed as a separable unit. No further take down of the operating group 50 is required for field maintenance and lubricatron.

For charging the machine gun a trigger group 114 is provided having a housing 116 mounted for sliding movement within a channel 118 along the bottom of the receiver 12 with a manual pistol grip 120 fixed to project downwardly from the housing 116. The trigger housing 116 has a fixed pin 122 serving as a pivot for a sear 124 biased upwardly by a spring 126 to engage a shoulder 128 on the bottom of the bolt carrier 82 for cocking it against the biasing force of the driving springs 90, 90 upon drawing the pistol grip 120 rearwardly and compressively loading the springs 90, 90.

For safety, the gun is normally handled and carried with the pistol grip 120 in a forward charging position indicated by broken lines 130 in FIG. 1. In this position an elongated ejection port 132 in the bottom of the receiver 12 is covered by the trigger group 114 and an attached stop plate 134 is slidably received within the channel 1 18. The stop plate 134 abuts against the buttstock 60 upon drawing the pistol grip 120 rearwardly to additionally limit its movement and establish a rear firing position for the trigger group 114. A latch 136 engages the receiver 12 to fix group 114 in firing position.

To prevent unintended release of the operating group 50 from the receiver 12 when the bolt carrier 82 is in sear and the driving springs 90, 90 are compressively loaded, the latch 108 for the operating group 50 is located in the receiver 12 so as to be entirely covered by the trigger group 114 in firing position.

Further economies are realized in the provision of a common shaft 138 to serve as a trigger pivot as well as a crossbolt safety. A trigger 140 is pivotally supported on the shaft 138 with a finger 142 extending forwardly for engagement with a rearwardly extending finger 144 on the sear 124. A trigger squeeze thus tends to pivot the sear 124 downwardly to ride off the shoulder 128 of the bolt carrier 82 and snap release it from its cocked position. The full diameter portion of the shaft 138, however, additionally serves as a crossbolt safety to normally engage a rear dog 146 on the sear 124 upon squeezing the trigger 140 whereby only limited sear movement is permitted, and such limited movement is insufficient to disengage the sear 124 from the bolt carrier 82. Upon pressing the shaft 138 to move laterally of the trigger housing 116, a relieved portion 148 (FIG.-

8) of the shaft 138 is brought into alignment with the path of travel of the sear dog 146 whereby trigger actuation will permit free movement of the sear 124 to release the bolt carrier 82.

Still another safety function is performed by the shaft 138 while being held in its safety" position by a spring-biased detent 150 engaging a cutout 152 in the shaft 138. While in safety" position, an end of the shaft 138 protrudes through a half moon-shaped opening 154 in the side wall of the receiver 12 to secure the trigger group 114 in firing position even though its latch 136 might be inadvertently released. Accordingly, the shaft 138 must be laterally offset, not only to condition the trigger 140 to disengage the sear 124 from the bolt carrier 82, but also to align slots 155, 155 in opposite end portions of the shaft 138 with bottom channel rails 118A, 118A to clear the receiver 12 for unlatching the trigger group 114 to permit charging.

Release of the bolt carrier 82 results in it being thrust forward under the driving force of the springs 90, 90 whereby a stripping and locking lug 156 on the bolt 52 housed in the bolt carrier 82 passes a cartridge stripping station to strip a round 158 from a disintegrating link cartridge belt 1611 prior to the round being chambered and fired after the bolt 52 is locked in closed battery position in the socket 28 of the barrel 10.

In closed battery the gas piston 80 is positioned in a chamber 161 of the gas porting head 16 with an inlet port 162 of the piston 80 in communication with the barrel bore via a gas conduit 164 which serves an an inlet to the chamber 161. A forwardly opening chamber 166 in the piston 80 receives a metered amount of compressed gases developed upon firing the gun during the time the conduit 164 is connected to the chamber 166 after the exiting bullet has passed the conduit 164 and before the piston 80 moves a sufficient distance rearwardly to cover or cut off the conduit 164. The driving force imparted to the piston 80 of the bolt assembly 62 is accordingly uniform irrespective of the climatic conditions or the type of ammunition being fired.

To minimize fouling of the gas recoil system, the gas porting head 16 is intentionally purged under high pressure shortly after gas cutoff by the piston 80. For this purpose an anti-fouling exhaust port 168 is provided in the gas porting head 16 and is shown as providing an opening circumferentially aligned in the chamber 161 with its gas conduit opening. To provide pressure buildup in the chamber 161 sufficient to drive the recoiling mass rearwardly to an extent limited by the buffer 58, the exhaust port 168 is initially covered by the piston during recoil. As the piston uncovers the port 168, the high pressure gases are purged from the chamber 161 and the gas conduit 164 is again exposed.

As the bolt assembly 62 travels rearwardly during its recoil cycle, the bolt assembly 62 strikes the recoil buffer 58 and compressively loads the buffer spring 70 while the energy is being dissipated. Assuming the trigger has been released, the shoulder 128 of the bolt carrier 82 sets up on the sear 124 to condition the gun to fire the next round. If the trigger 140 has not been released, the bolt carrier 82 clears the sear 124 during a forward or counter-recoil movement, and the springs 90, 90 drive the bolt assembly 62 forwardly again to repeat the operation of chambering and firing whereby a continuous burst of fire occurs until trigger release or until there are no more rounds to be fired, whichever first occurs;

Turning now to the feed system for successively advancing rounds to the stripping station for. subsequent chambering and firing, a feed tray 170 is shown nested into an upper opening 172 in the receiver 12. A cover 174 is associated with the feed tray 170, both of which are pivotally mounted on a pair of upstanding lugs 176, 176 on the barrel bearing block 32. A stepped flange 178 on the cover 174 engages a sliding latch 180 for maintaining the feed tray 170 in operative position.

Extending longitudinally of the feed tray 170 is a stripping slot 182 dimensioned somewhat narrower than a cartridge but sufficiently wide to permit the stripping lug 156 of the bolt 52 to pass through for stripping a round from the belt. The slot 182 in the feed tray 170 defines the cartridge stripping station for receiving and positioning rounds to be stripped from the belt. A cartridge guide 184. is suitably hinged for pivotal movement about an edge of the feed tray cover 174 to continuously press each cartridge downwardly into the stripping slot 182 under the biasing force of a torsion spring 186. A shaft 188 is fixed to ears 189 (FIG. 10) projecting from the cartridge guide 184 and serves to mount the torsion spring 186 which is biased against the cover 174. The same shaft 188supports a retaining pawl 190 and its torsion spring 192 for biasing the pawl downwardly toward the stripping slot 182. The pawl 190 projects through an opening 193 in the cartridge guide 184 for engaging links of the cartridge belt to prevent any tendency of the belt to back out under its own weight or to withdraw under the retracting force of the feed pawls.

It will be understood that the feed tray 170 and its cover 174 are suitably apertured to provide a link chute of a preselected size permitting ejection of empty belt links while preventing their tipping into the stripping slot 182 on the feed tray 170. Undesired forward movement of the links during stripping is prevented by a downwardly protruding lip 194 formed on the cartridge guide 184.

For advancing the cartridge belt while also permitting desired bottom ejection of spent cartridges, a pair of feed pawls 196, 196 are supported in offset relation to the operating group 50 for oscillating pivotal movement within a pair of transverse slots 198, 198 in the feed tray 170 communicating with its stripping slot 182. A torsion spring 200 is shown resiliently biasing the feed pawls 196 upwardly to engage each round in succession from below the feed tray 170 and advance the cartridge belt over a rounded side lip 202 of the tray 170 and into the stripping station. To further minimize any need for expensive machining of the side walls of the receiver 12, the feed pawls 196, 196 are drivingly connected outside the receiver 12 to a pivotable actuator 204.

The actuator 204 is shown having a curved rocker 206 joined to the feed pawls 196, 196 at one end of a horizontally extending arm 208 fixed to an inwardly ex tending lug 210 received within an aperture 212 of the receiver 12 and pivotally supported for rocking movement on the enlarged end 86 of the guide rod 72. The curved rocker 206 of the actuator 204 disposed outside the receiver 12 is configured to correspond with the projecting receiver side wall portion 76. Bearing surfaces for the curved rocker 206 of the actuator 204 are thereby provided by the outer side wall surface of the receiver 12 and an inside surface of a removable actuator cover 214 suitably secured to the outside of the receiver 12, preferably with the assistance of the lip 202 on the side of the feed tray 170.

To control oscillatory pivotal movement of the feed pawls 196, 196, two cam paths 216, 218 are formed directly on the bolt carrier 82. During the recoil cycle, a lower feed cam path 216 on the bolt carrier 82 provides a camming movement to a roller 220 rotatably supported on the actuator lug 210 to cause the feed pawls 196, 196 to move upwardly and engage a cartridge to feed the belt over the feed tray 170. During such feeding it is desired to overfeed the cartridge beyond the stripping slot 182 to ensure that the cartridge is fed sufficiently far irrespective of the weight of the belt or any variations in manufacturing tolerances. For this reason the feed cam path 216 is contoured to ensure that the following movement of the roller 220 during feeding will result in the feed pawls 196, 196 pushing each cartridge in succession past the stripping slot 182, preferably to an extent limited by a suitable cartridge stop (not shown) which can be integrally formed, e.g., on the feed tray cover 174.

Thereafter during the counter-recoil cycle, an upper return cam path 218 on the bolt carrier 82 contacts a wiper pad 222 on the actuator lug 210 to retract the feed pawls 196, 196 from the stripping slot 182. The retaining pawl 190 then engages a link of the belt and, with the assistance of the cartridge guide 184, the round is properly positioned in the stripping slot 182 with the feed pawls 196, 196 being in a lowered retracted position due to the contour of the cam path 218.

In accordance with still another feature of this invention, the bolt assembly not only strips a round from the belt but also chambers the round, locks it in battery, fires the round and extracts the cartridge substantially independently of the receiver 12 without any need for complex rails, rollers and other structures being mounted on the interior wall surfaces of the receiver as normally associated with machine guns of this type.

More specifically, the bolt 52 is housed within a longitudinally extending opening 224=within the bolt carrier 82 which moves the bolt 52 fore and aft of the receiver 12. As the bolt 52 moves forwardly during counter-recoil, it is fixed to the carrier 82 by an upright cam follower 226. The cam follower 226 is carried by and supported for vertical movement within the bolt carrier 82 and extends through a firing pin 228 received within a longitudinal chamber 230 in the bolt 52.

The firing pin 228 is provided with conical strikers 232 at its opposite longitudinal endsto permit it to be reversibly assembled within the bolt 52. Upon fitting the firing pin 228 into the bolt chamber 230 and aligning a transverse central opening 233 of the firing pin 228 (FIG. 4) with openings 234 and 236 in the top of the bolt 52 and the carrier 82, a cam follower spring 238 and the cam follower 226 are readily inserted through the bolt 52 and firing pin 228. The cam follower 226 is then retained in position within the bolt carrier 82 by a crosspin 240 fixed to the cam follower 226. The crosspin 240 extends laterally outwardly, through elongated oversize vertical openings (only one shown at 242) in opposite sides of the bolt carrier 82, and is dimensioned to position opposite free ends of the crosspin 240 adjacent the interior side wall surfaces 54, 56 of the receiver 12.

During stripping the cam follower 226 is biased by the spring 238 into an upper position within the top openings 234, 236 in the bolt 52 and bolt carrier 82 whereby the bolt 52, the bolt carrier 82 and the firing pin 228 move as an integral unit.

As the feed tray releases a round, permitting its removal from the stripping slot 182 upon engagement of the cartridge rim by the stripping lug 156 of the bolt 52, the round is prevented from jumping ahead by means of an upper linear guide lip 244. Lip 244 is spaced forwardly of the front flat face 246 of the bolt 52 to engage the rim of the round and ensure its movement will be in timed relation to the bolt 52 during chambering. No lateral forces are imposed on the round to be chambered during stripping; the only force exerted on the round is a downwardly directed biasing force of the cartridge guide 184.

To guide the forward tip of the round into the barrel 10, a downwardly extending tapered cartridge ramp 248 is formed in the rear barrel .socket 28. After the round passes the feed tray 170, the round will be trapped between the firing chamber 250 and the ramp 248 with a forwardly directed force being applied by the bolt 52. Once the round is received in the chamber 250, contoured guide surfaces of the chamber ensure proper seating of the round.

Immediately after the bolt 52 enters the socket 28 to seat the round, the free ends of the crosspin 240 engage contoured bottom edges of cam plates 252, 252 fixed to the interior side walls 54, 56 of the receiver 12 to retract the cam follower 226 into a lower or retracted position (FIG. 3) below the top opening 234 in the bolt 52 With the cam follower 226 in retracted position, the bolt 52 may be locked in battery and the chambered round fired after the bolt 52 has reached its forward limit position in locked battery. For this purpose, a curved slot 254 is formed in the bottom of the bolt 52 to provide a contoured cam surface engageable with the cam follower 226. Continued forward movement of the carrier 82 and its cam follower 226 rotates the bolt 52 (clockwise in FIG. 3) to engage the bolt locking lugs such as at 256 with complementary barrel lugs to lock the bolt 52 in battery.

To permit continued longitudinal movement of the bolt carrier 82, cam follower 226 and firing pin 228 past the locked battery position of the bolt 52, the slot 254 is dimensioned to providecontinued travel of the retracted cam follower 226 within the bolt 52 to cause the firing pin striker 232 to extend through a pin hole 248 in the bolt face 246 to engage the chambered round and tire the gun.

Initial rearward travel of the bolt carrier 82 relative to the locked bolt 52 provides a time delay allowing the release of gases from the barrel 10 after the bullet is out but before the gas conduit 164 is uncovered by the piston 80. Such delay minimizes gas blow back from the barrel 10 once the bolt 52 is counter-rotated by the cam follower 226 to unlock from the barrel socket 28.

recoil. Accordingly, should the rear end of thebolt 52 For service-free, fail-safe extraction, the bolt face I 246 additionally incorporates a fixed extractor lip 260. The latter extends in spaced relation to the bolt face 246 along an arc of about 120 included angle adjacent the bottom of the bolt face 246 for engaging the rim of the cartridge for withdrawing it from the chamber 250 during recoil.

To ensure that the spent cartridge will be retained within the extractor lip 260 and to minimize any tendency of the cartridge moving upwardly into the upper guide lip 244 during extraction, while yet permitting the cartridge to be tipped downwardly over the extractor lip 260, a cartridge retaining plunger 262 is mounted within the bolt face 246 to extend forwardly under the bias of a spring 264 trapped within the bolt 52. The plunger 262 is positioned above the striker pin hole 248 and projects over the extractor lip 260 for engagement with the cartridge during its extraction. The guide lip 244 will be seen to be spaced from the cartridge rim (shown in broken lines at 266 in FIG. 4) in noninterfering relation with the seated cartridge during extraction.

Before the bolt 52 leaves the barrel socket 28, the crosspin 240 will clear the cam plates 252, and the cam follower 226 will normally spring up into the top openings 234 and 236 in the bolt 52 and bolt carrier 82. To ensure proper seating of the cam follower 226 within the top opening 236 of the bolt carrier 82 during recoil, any possibility of excessive bolt rotation (due, e.g., to manufacturing variations and tolerances) is prevented by the provision of an inwardly directed guide lip or flange 268 projecting from one of the cam plates 252 for engaging and limiting rotation of a bolt lug such as 256.

An additional purpose is served by the guide flange 268 in preventing any possibility of the .bolt 52 stripping and firing a round out of battery should a malfunction of the spring 238 ever occur to misalign the bolt 52 within carrier 82. In such event, the rear end of the flange 268 will serve to interfere with a bolt lug to stop the bolt 52 and carrier 82 short before a round can be fully stripped from the feed tray 170.

A still further safety feature embodied in this invention is provided in positioning the buffer plunger 64 behind the bolt assembly 62 in operative alignment for be offset from the carrier 82 for any reason, the buffer plunger 64 'will positively engage both-members to ensure proper seating of the cam follower 226 to condition the bolt assembly 62 for the next counter-recoil cycle.

To provide positive ejection of spent cartridges through the bottom of the receiver 12 in timed relation to the rearward movement of the bolt carrier 82 during recoil, an ejector lever 270 is shown mounted above the ejection port 132 and connected to an ejector crank 272 through an interlocking drive. A pivot shaft 320 of the lever 270 is drivingly connected to a pivot shaft 274 of the crank 272. The pivot shafts 274, 320 are rotatably supported by a base member 276 fixed on top of the receiver 12 and, as best seen in FIG. 11, the shaft 274 of the crank 272 is coaxially received within an opening 322 for limited freedom of angular movement relative to the lever 270.

More specifically, the opening 322 receives an end portion of the shaft 274 and has an enlarged compartment of an hourglass cross-sectional shape defining contact surfaces 324, 326 for driving engagement with parallel flat shoulders 328, 330 formed on an intermediate portion of the crank shaft 274.

For continuously urging the lever 270 and its crank 272 in opposite angular directions to maintain the same in direct driving relation, a single torsion return spring 332 is shown (in phantom lines) coiled about crank shaft 274. Opposite ends 334, 336 of the spring 332 are fixed to the lever 270 and crank 272 respectively to continuously bias the same into direct driving engagement in its illustrated operative position shown in full lines in FIG. 11. A free end 280 of the lever 270 is located by the feed tray 170 in operative position and is resiliently maintained therein by an intermediate spring portion 338 biased into engagement with the base member 276 behind the ejector. By such construction, the feed tray 170 not only locates the lever 2 but also ensures that the crank 272 will be disposed in the path of movement of an actuating lug 278 on the bolt carrier 82 for driving engagement with the lug 278.

Accordingly, a positive mechanical ejector drive is effected by the driving force of the recoiling bolt carrier 82 in timed relation thereto irrespective of its velocity, while also eliminating any requirements for the use of springs serving as a driving force for cartridge ejection. Contact of the lug 278 with the crank 272 will force the crank into its rear broken line position shown at 340 in FIG. 11 to positively drive the lever 270 against its spring loading and swing its free end 280 downwardly to strike a forward end of the extracted cartridge and simply bat it out over the bolt extractor lip 260 through an opening in the bolt carrier 82 and the receiver ejection port 132. This action further loads the spring 332 engaged with the base member 276 to return the ejector to its operative position with the free end 280 of the lever 270 abutting the feed tray after the lug 278 has passed by the crank 272.

On counter-recoil, the above-described interlocking connection between the lever 270 and its crank 272 permits free travel of the crank 272 to its forward limit position (shown in broken lines at 342) established by contact engagement between the crank shoulders 328,

330 and surfaces 344, 346 of the hourglass opening 322. As the lug 278 passes the crank 272, the lever 270 remains in position during pivotal movement of the crank 272 which is returned by the spring 332 into operative position to be automatically re-engaged in driving engagement with the lever 270.

The base member 276 on which the ejector mechanism is supported also serves as a mount for a rear sight 284. A rear peep sight member 286 is mounted for vertical movement on a sight bracket 288 having a threaded post 290 fixed relative to the sight member 286 and extending through an apertured mounting lug 292 thereon. Elevation adjustment of the sight is effected by an adjusting nut 294 threaded onto the post 290 in engagement with the mounting lug 292. For lateral windage adjustment of the sight, a windage screw 296 is engaged within a threaded opening 298 in the bottom of the bracket 288 for selectively moving the bracket and its peep sight 286 in a selected lateral direction by rotating an adjusting knob 300 fixed to an end of the windage screw 296. The latter serves as a pivot for the bracket 288 and is supported within two upstanding ears 302 on the base member 276.

To ensure that zero backlash occurs during elevational adjustment of the sight 284, its mounting lug 292 is continuously biased into engagement with the elevation adjusting nut 294 by a spring 304 coiled about the post 290 between the lug 292 and the bracket 288. The windage adjustment is likewise maintained in a selected position with zero backlash upon screw adjustment. Spring-loaded ball detents (only one shown at 306 in FIG. 7) are carried in the adjusting knob 300 for engagement within cavities such as that shown at 308 formed in a confronting face of the car 302. Springs such as 310 thus continuously exert a loading force on the windage screw 296 to urge its shoulder 312 into abutment with the ear 302 of the base member 276 to resiliently maintain the windage screw 296 against unintended movement and effectively fix it relative to the bracket 288 so as to achieve precision windage adjustment with zero backlash. Upon seating in the cavities 308, the ball detents 306 provide an audible click for indicating a predetermined windage adjustment; if desired, a similar adjustment indicator may be incorporated in the adjustment for sight elevation.

A single leaf spring 314 supported on the base member 276 serves to maintain the sight 284 in both its illustrated upright operative position as well as in an inoperative position wherein the sight 284 is folded down over the spring 314 onto the base member 276. A forward end of the spring 314 is fixed to the base member 276 and an opposite free end continuously exerts an upward biasing force to one of two flat surfaces 316, 318 formed on the base of the sight bracket 288 to selectively maintain the sight in either operative or folded positions respectively.

It will also be noted that the base member 276 mounted on the top of the receiver 12 not only provides a mount for the rear sight 284 but additionally serves to support the sliding latch 180 for holding down the feed tray 170 and its cover 174 and is also used to retain the actuator cover 214 in place when the feed tray 170 is raised.

In view of the foregoing it will be seen that the construction of the receiver 12 is considerably simplified and essentially serves only as a cover which can be inexpensively manufactured in a mass production operation. Only the cam plates 252 and the barrel bearing block 32 need be fixed inside the receiver. The simplicity of the receiver design and the construction of the unitary bolt and bolt drive assembly results in an exceptionally compact, fail-safe operating group 50. In addition, the integral operating group 50, being readily removable as a separable unit by the simple expedient of pushing down a single latch 108 immediately exposes all parts of the operating group 50 upon removal from the receiver 12 in a one step operation for quick and easy field maintenance and lubrication.

As will be apparent to persons skilled in the art, various modifications, adaptions and variations of the foregoing specific disclosure can be made'without departing from the teachings of the present invention.

We claim:

1. A gun comprising a receiver, an operating group mounted for operation within the receiver, the operating group including a bolt and bolt carrier assembly and a recoil buffer assembly, retaining means releasably retaining the bolt and bolt carrier assembly in assembled relation to the recoil buffer assembly for facile disassembly and reassembly of the operating group, and a single latch removably securing the operating group to the receiver in assembled relation, the operating group being removable from the receiver as a single separable unit.

2. The gun of claim 1 further including a trigger group slidably mounted along the bottom of the receiver for charging the bolt and bolt carrier assembly, the trigger group being movable between a forward charged position and a rearward firing position, the trigger group in firing position overlying and covering the latch to prevent unintended unlatching.

3. The gun of claim 2 wherein the trigger group includes a pivotable trigger and a pivot shaft for the trigger, the trigger shaft being movable laterally of the receiver when the trigger group is in firing position for selective locking engagement and disengagement with the receiver, the trigger shaft permitting trigger actuation only when it is disengaged from the receiver.

4. The gun of claim 2 wherein the trigger group includes a downwardly extending pistol grip serving as a charging handle for the gun.

5. The gun of claim 1 further including a barrel on the receiver, and wherein the bolt and bolt carrier assembly includes a bolt having a cam path formed therein, a reciprocable carrier supporting the bolt for longitudinal and angular movement relative to the receiver, a firing pin received within the bolt and supported for movement with the bolt carrier, and a cam follower carried by the bolt carrier, the cam follower being movable in relation to the bolt along its cam path to move the bolt longitudinally and angularly relative to the bolt carrier for locking and unlocking the bolt in battery with the barrel during longitudinal reciprocable movement of the bolt carrier.

6. The gun of claim 5 wherein the recoil buffer assembly includes a reciprocable plunger positioned in operative alignment with both the bolt and bolt carrier for engagement with both the bolt and bolt carrier during recoil.

7. The gun of claim 5 further including a fixed extractor lip on the face of the bolt.

8. The gun of claim 7 wherein the bolt includes a cartridge retaining plunger projecting outwardly from the bolt face above the extractor lip.

9. The gun of claim wherein the cam follower fixes the firing pin to the carrier for movement therewith.

10. The gun of claim 5 wherein the firing pin includes an elongated body having a striker at opposite ends thereof for reversible positioning within the bolt.

11. The gun of claim 5 wherein the cam follower is movable within the bolt carrier between a first position fixing the bolt to the bolt carrier and a second position permitting said relative movement between the bolt and bolt carrier for lockingand unlocking the bolt in battery responsive to relative movement of the cam follower along the cam path of the bolt.

12. The gun of claim 11 further including cam plate means fixed within the receiver, and a pin fixed to the cam follower and engageable with the cam plate means for moving the cam follower between its said first and second positions.

13. The gun of claim 12 wherein the bolt includes locking lugs, and wherein the cam plate means includes a lip directed inwardly a sufficient distance to engage a bolt lug for limiting angular unlocking movements of the bolt.

14. The gun of claim 1 further including two guide rods removably mounted within the receiver, a gas recoil cylinder, and a piston integrally secured to the bolt and bolt carrier assembly for reciprocating movement within the cylinder, the two guide rods and the gas cylinder providing bearing surfaces for supporting the bolt and bolt carrier assembly for longitudinal reciprocable movement relative to the receiver.

, 15. The gun of claim 1 further comprising a barrel detachably insertable into the receiver, and an automatically engageable self-aligning and self-locking barrel and receiver latch assembly including a movable first latch member on one of the barrel and receiver members, a fixed second latch member on the other of the barrel and receiver members, the first andsecond latch members having cooperating barrel alignment means for automatically aligning and securing the barrel and receiver against relative rotation, and releasable means continuously biasing the first latch member into locked assembly with the second latch member and permitting automatic engagement of the first and second latch members upon inserting the barrel into the receiver in aligned relation therewith as determined by the cooperating barrel alignment means.

16. A gun comprising an elongated receiver, a reciprocable bolt carrier and a recoil buffer assembly releasably retained in assembly therewith, a gas cylinder extending longitudinally of the receiver in fixed relation thereto; guide rod means mounted within the receiver to extend longitudinally thereof, and a gas piston fixed to the bolt carrier for operation within the cylinder, the guide rod means and the gas cylinder providing bearing surfaces supporting the bolt carrier for reciprocating longitudinal movement relative to the receiver, means permitting the bolt carrier, recoil buffer and the guide rod means to be removed as a single separable unit from the receiver.

17. The gun of claim 16 wherein the buffer includes a reciprocable plunger engageable with the bolt carrier for absorbing shock loads imposed during recoil, and wherein the guide rod means comprises two guide rods on opposite sides of the bolt carrier in outboard parallel relation to the plunger, the guide rods each having a spring coiled thereabout in driving relation to the bolt carrier.

18. The gun of claim 16 further including a single latch maintaining the bolt carrier, recoil buffer and the guide rod means in assembled relation with the receiver and the gas cylinder.

19. The gun of claim 16 wherein the receiver includes a bottom opening adjacent its rearward end, the buffer includes a cavity formed in a bottom portion thereof for communication with the opening in the receiver, a pushbutton latch is received in the buffer cavity having an end portion spring biased outwardly in interfering relation with the receiver, and wherein a manual charging handle is supported for sliding movement on the bottom of the receiver between a forward charged position and a rearward firing position, the charging handle in firing position covering the latch to prevent inadvertent release of the latch.

20. The gun of claim 11 wherein the receiver includes a cartridge belt stripping station, cartridge belt advancing means including movable feed pawl means for advancing a cartridge belt to the stripping station, and cam path means on the bolt carrier and engageable with the cartridge belt advancing means to pivot the feed pawl means in opposite angular directions for advancing the cartridge belt to the stripping station in timed relation to reciprocating movement of the bolt carrier.

21. The gun of claim 16 further comprising a barrel on the receiver, gas conduit means in continuous open communication with the barrel and opening into the cylinder, the gas piston reciprocable in the cylinder and having an inlet port for connecting the gas conduit means to the cylinder for driving the bolt carrier rearwardly of the receiver responsive to firing of a cartridge, the piston covering the gas conduit means to effect temporary gas cutoff responsive to a predetermined rearward driving force imparted to the piston by the gases developed by firing the gun, and an anti-fouling exhaust port in the cylinder covered by the piston during firing for purging gases under high pressure from the cylinder after gas cutoff is effected by the piston covering the gas conduit means.

22. The gun of claim 21 wherein a hand grip is fixed to a forward portion of the receiver, and wherein the gas cylinder is locked in assembled relation to the receiver by the hand grip.

23. The gun of claim 21 wherein a gas porting head is fixed to the barrel and includes a cylindrical chamber having an opening connected to the gas conduit means for communicating with the barrel, wherein a gas cylinder secured to the receiver is fitted into the chamber, the gas cylinder and chamber jointly constituting the gas cylinder means, and wherein the antifouling exhaust port is formed in the gas porting head and opens into its chamber in substantial circumferential alignment with the chamber opening communicating with the barrel.

24. The gun of claim 20 wherein guide rod means extends longitudinally within the receiver and supports the bolt carrier for movement therein, and wherein the cartridge belt advancing means further includes an actuator drivingly connected to the feed pawl means, the

guide rod means providing a pivot shaft for the actuator.

25. The gun of claim 20 wherein the feed pawl means is supported for pivotal movement in offset relation to the bolt carrier, and wherein the bottom of the receiver is apertured to provide an ejection port for spent cartridges.

26. The gun of claim 20 wherein the cam path means on the bolt carrier is contoured to provide overtravel of the feed pawl means in one angular direction to overfeed each cartridge past the stripping station before the feed pawl means is retracted in an opposite angular direction to ensure cartridge stripping irrespective of the weight of the belt being fed, and wherein the cartridge belt advancing means further includes retaining pawl means for engaging the belt to prevent withdrawal of a cartridge from the stripping station under the weight of the belt.

27. The gun of claim 24 wherein the actuator extends outside the receiver, the feed pawl means being offset from the guide rod means and fixed to the actuator outside the receiver, and wherein a cover is provided for the actuator, an outside surface portion of the receiver and an inside surface portion of the cover serving as bearing surfaces for the actuator.

28. The gun of claim 25 further including an ejecto mounted above the ejection port for pivotal movement toward and away from the same, and wherein the bolt cam'er additionally carries an actuating lug for actuating the ejector to positively eject spent cartridges outwardly through the bottom ejection port of the receiver responsive to the driving force of the bolt carrier but independently of its velocity.

29. The gun of claim 15 further including a carrying handle fixed to the barrel.

30. The gun of claim 15 wherein the releasable means comprises a spring seated between said one of the barrel and receiver members and the first latch means for continuously urging it into locking engagement with the second latch member.

31. The gun of claim 15 wherein the second latch member comprises a boss extending circumferentially about the barrel, and wherein the first latch member is supported for pivotal movement on the receiver for engagement with the boss on the barrel.

32. The gun of claim 37 wherein the boss includes a slot therethrough at the top of the barrel, and wherein the first latch member includes a boss engaging lip and an upright web extending rearwardly thereof for receipt within the slot in the boss for automatically aligning and securing the barrel against rotation relative to the receiver, the slot in the boss and the web of the first latch member constituting said barrel alignment means. 

1. A gun comprising a receiver, an operating group mounted for operation within the receiver, the operating group including a bolt and bolt carrier assembly and a recoil buffer assembly, retaining means releasably retaining the bolt and bolt carrier assembly in assembled relation to the recoil buffer assembly for facile disassembly and reassembly of the operating group, and a single latch removably securing the operating group to the receiver in assembled relation, the operAting group being removable from the receiver as a single separable unit.
 2. The gun of claim 1 further including a trigger group slidably mounted along the bottom of the receiver for charging the bolt and bolt carrier assembly, the trigger group being movable between a forward charged position and a rearward firing position, the trigger group in firing position overlying and covering the latch to prevent unintended unlatching.
 3. The gun of claim 2 wherein the trigger group includes a pivotable trigger and a pivot shaft for the trigger, the trigger shaft being movable laterally of the receiver when the trigger group is in firing position for selective locking engagement and disengagement with the receiver, the trigger shaft permitting trigger actuation only when it is disengaged from the receiver.
 4. The gun of claim 2 wherein the trigger group includes a downwardly extending pistol grip serving as a charging handle for the gun.
 5. The gun of claim 1 further including a barrel on the receiver, and wherein the bolt and bolt carrier assembly includes a bolt having a cam path formed therein, a reciprocable carrier supporting the bolt for longitudinal and angular movement relative to the receiver, a firing pin received within the bolt and supported for movement with the bolt carrier, and a cam follower carried by the bolt carrier, the cam follower being movable in relation to the bolt along its cam path to move the bolt longitudinally and angularly relative to the bolt carrier for locking and unlocking the bolt in battery with the barrel during longitudinal reciprocable movement of the bolt carrier.
 6. The gun of claim 5 wherein the recoil buffer assembly includes a reciprocable plunger positioned in operative alignment with both the bolt and bolt carrier for engagement with both the bolt and bolt carrier during recoil.
 7. The gun of claim 5 further including a fixed extractor lip on the face of the bolt.
 8. The gun of claim 7 wherein the bolt includes a cartridge retaining plunger projecting outwardly from the bolt face above the extractor lip.
 9. The gun of claim 5 wherein the cam follower fixes the firing pin to the carrier for movement therewith.
 10. The gun of claim 5 wherein the firing pin includes an elongated body having a striker at opposite ends thereof for reversible positioning within the bolt.
 11. The gun of claim 5 wherein the cam follower is movable within the bolt carrier between a first position fixing the bolt to the bolt carrier and a second position permitting said relative movement between the bolt and bolt carrier for locking and unlocking the bolt in battery responsive to relative movement of the cam follower along the cam path of the bolt.
 12. The gun of claim 11 further including cam plate means fixed within the receiver, and a pin fixed to the cam follower and engageable with the cam plate means for moving the cam follower between its said first and second positions.
 13. The gun of claim 12 wherein the bolt includes locking lugs, and wherein the cam plate means includes a lip directed inwardly a sufficient distance to engage a bolt lug for limiting angular unlocking movements of the bolt.
 14. The gun of claim 1 further including two guide rods removably mounted within the receiver, a gas recoil cylinder, and a piston integrally secured to the bolt and bolt carrier assembly for reciprocating movement within the cylinder, the two guide rods and the gas cylinder providing bearing surfaces for supporting the bolt and bolt carrier assembly for longitudinal reciprocable movement relative to the receiver.
 15. The gun of claim 1 further comprising a barrel detachably insertable into the receiver, and an automatically engageable self-aligning and self-locking barrel and receiver latch assembly including a movable first latch member on one of the barrel and receiver members, a fixed second latch member on the other of the barrel and receiver members, the first and second latch members having cooperating barrel aliGnment means for automatically aligning and securing the barrel and receiver against relative rotation, and releasable means continuously biasing the first latch member into locked assembly with the second latch member and permitting automatic engagement of the first and second latch members upon inserting the barrel into the receiver in aligned relation therewith as determined by the cooperating barrel alignment means.
 16. A gun comprising an elongated receiver, a reciprocable bolt carrier and a recoil buffer assembly releasably retained in assembly therewith, a gas cylinder extending longitudinally of the receiver in fixed relation thereto; guide rod means mounted within the receiver to extend longitudinally thereof, and a gas piston fixed to the bolt carrier for operation within the cylinder, the guide rod means and the gas cylinder providing bearing surfaces supporting the bolt carrier for reciprocating longitudinal movement relative to the receiver, means permitting the bolt carrier, recoil buffer and the guide rod means to be removed as a single separable unit from the receiver.
 17. The gun of claim 16 wherein the buffer includes a reciprocable plunger engageable with the bolt carrier for absorbing shock loads imposed during recoil, and wherein the guide rod means comprises two guide rods on opposite sides of the bolt carrier in outboard parallel relation to the plunger, the guide rods each having a spring coiled thereabout in driving relation to the bolt carrier.
 18. The gun of claim 16 further including a single latch maintaining the bolt carrier, recoil buffer and the guide rod means in assembled relation with the receiver and the gas cylinder.
 19. The gun of claim 16 wherein the receiver includes a bottom opening adjacent its rearward end, the buffer includes a cavity formed in a bottom portion thereof for communication with the opening in the receiver, a pushbutton latch is received in the buffer cavity having an end portion spring biased outwardly in interfering relation with the receiver, and wherein a manual charging handle is supported for sliding movement on the bottom of the receiver between a forward charged position and a rearward firing position, the charging handle in firing position covering the latch to prevent inadvertent release of the latch.
 20. The gun of claim 11 wherein the receiver includes a cartridge belt stripping station, cartridge belt advancing means including movable feed pawl means for advancing a cartridge belt to the stripping station, and cam path means on the bolt carrier and engageable with the cartridge belt advancing means to pivot the feed pawl means in opposite angular directions for advancing the cartridge belt to the stripping station in timed relation to reciprocating movement of the bolt carrier.
 21. The gun of claim 16 further comprising a barrel on the receiver, gas conduit means in continuous open communication with the barrel and opening into the cylinder, the gas piston reciprocable in the cylinder and having an inlet port for connecting the gas conduit means to the cylinder for driving the bolt carrier rearwardly of the receiver responsive to firing of a cartridge, the piston covering the gas conduit means to effect temporary gas cutoff responsive to a predetermined rearward driving force imparted to the piston by the gases developed by firing the gun, and an anti-fouling exhaust port in the cylinder covered by the piston during firing for purging gases under high pressure from the cylinder after gas cutoff is effected by the piston covering the gas conduit means.
 22. The gun of claim 21 wherein a hand grip is fixed to a forward portion of the receiver, and wherein the gas cylinder is locked in assembled relation to the receiver by the hand grip.
 23. The gun of claim 21 wherein a gas porting head is fixed to the barrel and includes a cylindrical chamber having an opening connected to the gas conduit means for communicating with the barrel, wherein a gas cylinder secured to the receiver is fitted into the chamber, the gas cylinder and chamber jointly constituting the gas cylinder means, and wherein the anti-fouling exhaust port is formed in the gas porting head and opens into its chamber in substantial circumferential alignment with the chamber opening communicating with the barrel.
 24. The gun of claim 20 wherein guide rod means extends longitudinally within the receiver and supports the bolt carrier for movement therein, and wherein the cartridge belt advancing means further includes an actuator drivingly connected to the feed pawl means, the guide rod means providing a pivot shaft for the actuator.
 25. The gun of claim 20 wherein the feed pawl means is supported for pivotal movement in offset relation to the bolt carrier, and wherein the bottom of the receiver is apertured to provide an ejection port for spent cartridges.
 26. The gun of claim 20 wherein the cam path means on the bolt carrier is contoured to provide overtravel of the feed pawl means in one angular direction to overfeed each cartridge past the stripping station before the feed pawl means is retracted in an opposite angular direction to ensure cartridge stripping irrespective of the weight of the belt being fed, and wherein the cartridge belt advancing means further includes retaining pawl means for engaging the belt to prevent withdrawal of a cartridge from the stripping station under the weight of the belt.
 27. The gun of claim 24 wherein the actuator extends outside the receiver, the feed pawl means being offset from the guide rod means and fixed to the actuator outside the receiver, and wherein a cover is provided for the actuator, an outside surface portion of the receiver and an inside surface portion of the cover serving as bearing surfaces for the actuator.
 28. The gun of claim 25 further including an ejector mounted above the ejection port for pivotal movement toward and away from the same, and wherein the bolt carrier additionally carries an actuating lug for actuating the ejector to positively eject spent cartridges outwardly through the bottom ejection port of the receiver responsive to the driving force of the bolt carrier but independently of its velocity.
 29. The gun of claim 15 further including a carrying handle fixed to the barrel.
 30. The gun of claim 15 wherein the releasable means comprises a spring seated between said one of the barrel and receiver members and the first latch means for continuously urging it into locking engagement with the second latch member.
 31. The gun of claim 15 wherein the second latch member comprises a boss extending circumferentially about the barrel, and wherein the first latch member is supported for pivotal movement on the receiver for engagement with the boss on the barrel.
 32. The gun of claim 37 wherein the boss includes a slot therethrough at the top of the barrel, and wherein the first latch member includes a boss engaging lip and an upright web extending rearwardly thereof for receipt within the slot in the boss for automatically aligning and securing the barrel against rotation relative to the receiver, the slot in the boss and the web of the first latch member constituting said barrel alignment means. 